Aslam S. Hassan

Specific Changes of Bile Acid Metabolism in Spontaneously Diabetic Wistar Rats

Abstract Bile acid metabolism has been investigated in a newly described animal model depicting juvenile human diabetes (spontaneously diabetic Wistar (BB) rat) and compared to normoglycemic control from the Wistar strain. Diabetic animals used were on insulin treatment except for the last 24 hr. The plasma glucose levels (mg%) of diabetic rat (D) was significantly higher than control rats (C) (150 ± 35 in C vs 340 ± 32 in D). The total bile acid pool (mg/100 g) in D was significantly (P < 0.05) higher when compared to C (9.0 ± 0.8 in C vs 14.9 ± 1.7 in D). The pool of cholic acid was significantly (P < 0.05) increased while that of chenodeoxycholic acid was significantly (P < 0.05) decreased (cholic acid: 5.9 ± 0.45 in C vs 10.06 ± 1.2 in D; chenodeoxycholic 0.90 ± 0.1 in C vs 0.57 ± 0.06 in D). This increased the cholic/chenodeoxycholic acid ratios from 6.6 ± 0.4 in controls to 19.3 ± 2.4 in diabetic rats. These studies have shown diverse alteration in the concentration of the two primary bile acids in the diabetic state.

Persistent enhancement of bile acid synthesis in guinea pigs following stimulation of cholesterol catabolism in neonatal life.

Cholesterol catabolism to bile acids was stimulated in neonatal guinea pigs by feeding 1.11% cholestyramine (CT)-containing diet for 8 weeks. The animals were then switched to standard laboratory diet for an additional 4 weeks. At the end of the laboratory diet period: a) CT-pre-treated guinea pigs continued to excrete significantly higher (p less than 0.05) amounts of bile acids, b) the activity of hepatic 7 alpha-hydroxylase was significantly elevated (p less than 0.01) in CT-pre-treated animals, and c) isolated hepatocytes from CT-pre-treated guinea pigs secreted significantly higher (p less than 0.05) amounts of bile acid when compared to controls during a 4-hour incubation. These data provide biochemical support for our contention that stimulation of cholesterol catabolism during neonatal life can have effects that persist into adult life.

Abnormal bile acid pool and composition in neonates of spontaneously diabetic Wistar BB rats and its change during development.

Streptozotocin-induced diabetes during pregnancy in rats causes a decrease in primary bile acid pool in neonates. To rule out direct drug effect on the fetus as the basis for this change, studies of bile acid pool and composition at birth and during subsequent development was carried out in neonates of spontaneously diabetic Wistar BB rats and compared to control neonates. The cholic acid pool in neonates of diabetic rats was lower when compared to control neonates at birth. The pool of secondary bile acids was markedly increased in neonates of diabetic rats, with increases in lithocholic and 3 beta,12 alpha-dihydroxycholanoic acid. With age, the cholic acid pool of neonates from diabetic rats was increased and at 3 months of age it was actually higher than in control neonates. The pool of chenodeoxycholic at diabetes onset age was lower in neonates of diabetic rats. HDL-cholesterol was lower in neonates of diabetic rats at 1 week, but this reversed at 3 months of age. These studies firmly establish that neonates of diabetic rats have abnormal bile acid pool and composition at birth which changes to adult diabetic pattern with age.

Effect of diabetes during pregnancy on maternal and neonatal bile acid metabolism in the rat.

Abstract The effect of streptozotocin-induced diabetes in pregnant rats, on subsequent maternal and neonatal bile acid metabolism was investigated. Plasma glucose levels (mg%) of diabetic pregnant (DP) rats was significantly greater (p < 0.05) in comparison to control pregnant (CP) rats. Total bile acid pool (mg/100g body wt) in DP was significantly higher (p < 0.05) when compared to CP (DP, 29.42 ± 4.44 vs 8.14 ± 1.13 in CP) with a marked increase in cholic acid pool size in DP (DP, 22.65 ± 3.33 vs 3.50 ± 0.48 CP, p < 0.05). The fecal excretion of bile acid was significantly lower (p < 0.05) in DP rats when compared to CP rats. Thin-layer chromatographic analysis of bile acid conjugates at postpartum revealed a significant increase in glycine conjugates in bile from DP rats. Examination of the cholic acid pool (μg/100 g body wt) in neonates (2 days old) derived from the two groups of rats indicated a strikingly reduced pool of cholic acid in neonates derived from diabetic mothers (neonates from DP 853.45 μ 213.98 vs 3690.86 μ 797.26 in CP,p < 0.05). Plasma cholesterol levels (mg%) in neonates of diabetic mothers was also significantly (p < 0.05) reduced. This study demonstrates that the diabetic state during pregnancy not only alters maternal bile acid metabolism, but also affects fetal bile acid metabolism in utero such that the effects may persist into neonatal life.

Development of Bile Acid Biogenesis in the Rat: Effect of Neonatal Thyroidectomy, Adrenalectomy, and Streptozotocin-Induced Diabetes

Effect of neonatal thyroidectomy, adrenalectomy and streptozotocin-induced diabetes in rats on the bile acid pool size and composition at weaning was examined. Adrenalectomy caused a significant (p less than 0.05) decrease in the total bile acid pool with significant reductions (p less than 0.05) in both cholic and chenodeoxycholic acids. Thyroidectomy on the other hand caused a specific decrease (p less than 0.05) in chenodeoxycholic acid pool. Streptozotocin-induced diabetes caused (a) a decrease (p less than 0.05) in total bile acid pool with a significant (p less than 0.05) reduction in chenodeoxycholic acid, and (b) an increase in plasma cholesterol levels.

Effect of feeding beta-sitosterol alone or in combination with cholestyramine during early life on subsequent response to cholesterol challenge in adult life in guinea-pigs.

The effect of feeding 20 g beta-sitosterol/kg alone or in combination with cholestyramine (20 g/kg) during neonatal life of guinea-pigs on their subsequent response to a dietary cholesterol challenge in adult life was examined. 2. beta-Sitosterol pretreated animals showed higher plasma cholesterol values following 2 weeks on a cholesterol challenge (2-5 g/kg) diet, but did not differ significantly from control values for the remainder of the cholesterol challenge period. 3. Guinea-pigs pretreated with beta-sitosterol plus cholestyramine, on the other hand, showed a marked increase in plasma cholesterol levels over those of controls during the cholesterol challenge period, and this hyper-responder behaviour was maintained throughout the study period. 4. Despite the increase in plasma cholesterol, beta-sitosterol plus cholestyramine pretreated animals excreted significantly (P less than 0.05) greater amounts of bile acids and total sterols. 5. These findings demonstrate that neonatal pretreatment with beta-sitosterol plus cholestyramine has detrimental effects on the handling of a cholesterol challenge in adult life, and does not achieve the beneficial effect previously noted with pretreatment with cholestyramine alone.

Bile acids in the fetal rat: Effect of maternal bile duct ligation ☆

The effect of bile duct ligation during pregnancy in rats (thereby increasing maternal plasma bile acids levels) on the bile acid content and composition in the fetus was examined. In spite of 30-fold increase in maternal plasma cholic acid, the bile acid content in the fetus of bile duct ligated rats was significantly lower (p less than 0.05) with a significant reduction in cholic acid content. Plasma cholesterol levels of fetuses from bile duct ligated rats were also significantly lower (p less than 0.05). In addition to the commonly expected bile acids, gas-liquid chromatographic analysis of the fetal bile acid pool showed peaks corresponding to several secondary bile acids. These results suggest that the transfer of primary bile acids of maternal origin into the fetus is minimal.

Feeding-Induced Regulation of Cholesterol Metabolism: A Unified Proposal

It is generally agreed that the liver is a key organ in the maintenance of cholesterol homeostasis. Although species variations do exist (1), there is no question that the liver makes a very significant contribution to whole body cholesterol synthesis (2). Indeed, recent studies in the rat suggest that the liver may be responsible for the synthesis of greater than 80% of newly synthesized cholesterol in the body (3). It is also well established that the liver is a major site of uptake of cholesterol from lipoprotein particles (1). The acquisition of cholesterol from lipoprotein particles is a process which occurs via both receptor-independent and receptor-dependent pathways (1). The latter pathway is considered to be more important not only from a quantitative standpoint (1) but also because of the fact that the activity of certain receptors is regulated by the hepatic demand for cholesterol (4). These observations, combined with the fact that the liver is the major site (if not the only site) of synthesis of bile acid, the chief catabolic product of cholesterol (5), suggest that the key hepatic enzymes involved in cholesterol metabolism must be very carefully regulated in order to maintain cholesterol homeostasis. Hepatic cholesterol 7α-hydroxylase (CH-7A, EC 1.14.13.7) and β-hydroxy-β-methyl-glutaryl coenzyme A reductase (HMGCoA reductase, EC 1.1.1.34) are the two key enzymes of cholesterol metabolism in the liver (2, 6). HMGCoA reductase is the rate-limiting enzyme in the biosynthesis of cholesterol (2), while CH-7A is considered to be the rate-limiting enzyme in the biosynthesis of bile acids from cholesterol (6). Since cholesterol is the precursor for bile acid biosynthesis, changes in the rate of synthesis of bile acids, in general, affect the rate of biosynthesis of cholesterol (6). Thus, the two enzymes are regulated in a coordinated manner (6).

Effect of maternal diabetes on fetal bile acid metabolism in the rat

Abstract Effect of diabetes induced by streptozotocin during pregnancy on fetal bile acid metabolism was investigated in the rat. Serum bile acid levels of diabetic pregnant rats were higher than those of control pregnant rats. Total pool of primary bile acids (cholic and chenodeoxycholic acids) in fetuses of diabetic mothers was significantly lower than that of control fetuses. However, the concentration of secondary bile acids, i.e., lithocholic, deoxycholic, and 3β, 12α-dihydroxycholanoic acids, was significantly higher in fetuses of diabetic mothers. These results suggest that the alteration in bile acid metabolism noted previously (4) in neonates of diabetic mothers is probably a manifestation of the effect of maternal diabetes at the fetal level.

Effect of Chenodeoxycholic Acid Feeding during Gestation in the Rat on Bile Acid Metabolism and Liver Morphology

Abstract Chenodeoxycholic acid (CDCA) was fed to pregnant rats at the 0.25% level in the diet from Day 11 of gestation to delivery in order to evaluate the effects on (1) maternal tissue bile acid composition, (2) neonatal tissue bile acid composition and cholesterol-7α-hydroxylase activity, and (3) maternal, neonatal, and postnatal liver morphology. Feeding CDCA increased maternal lithocholic acid while significantly decreasing deoxycholic acid, cholic acid, and total bile acids. Feeding CDCA resulted in a significantly higher chenodeoxycholic acid pool in the neonates while neonatal plasma cholesterol and the 7α-hydroxylation of cholesterol was not significantly affected. Morphological examination of maternal, neonatal, and postnatal rat liver revealed no significant hepatotoxicity. This investigation has shown that (a) neonates of CDCA fed dams have a significantly greater pool of CDCA, suggesting maternal-to-fetal transfer of dihydroxy bile acids, (b) neonatal cholesterol-7α-hydroxylase activity and total tissue bile acid pools are not significantly altered by increased pool of CDCA, and (c) no hepatotoxic effects on maternal, neonatal, and postnatal livers were evident with gestational feeding of CDCA at the 0.25% level in the rat.